Radio navigation emulating GPS system

ABSTRACT

The present invention provides a radio navigation emulating GPS device. In one embodiment, the radio navigation emulating GPS device receives an identifier associated with a conventional radio navaid. The present radio navigation emulating GPS device then retrieves latitude and longitude information corresponding to the received conventional radio navaid from a database. A satellite based position information system generates position information for the aircraft on which the present radio navigation emulating GPS device is disposed. The present radio navigation emulating GPS device then generates navigation information for the aircraft using the retrieved latitude and longitude information and the satellite based position information for the aircraft. The present radio navigation emulating GPS device then presents the navigation information in a manner which emulates the presentation of navigation information generated by a conventional radio navigation device. The entire emulation process is transparent to the user of the present radio navigation emulating GPS device.

This application is a continuation of Ser. No. 09/186,777 filed Nov. 4,1998 U.S. Pat. No. 6,163,753 which is a continuation of Ser. No.08/665,318 filed Jun. 17, 1996 U.S. Pat. No. 5,957,995.

TECHNICAL FIELD

The present relates to navigation aids. In particular, the presentinvention pertains to aviation navigation aids.

BACKGROUND ART

For the past 40 years, air navigation has primarily consisted of variousforms of radio direction finding devices. With these devices, navigationinformation is transmitted from a fixed ground station and received byairborne aircraft equipped with the appropriate receivers. Each groundtransmitter has a unique radio frequency associated therewith. Tonavigate an aircraft, the pilot dials or tunes a receiver to thefrequency associated with the ground based transmitter, and then fliesthe aircraft towards the transmitter. Once the pilot reaches thetransmitter, the pilot tunes in the frequency of the next transmitteralong the pilot's chosen route. Identifiers for the ground transmittersare typically displayed to the pilot as TO navaids and FROM navaids. Anidentifier for the ground transmitter towards which the aircraft isheading is marked as the TO waypoint or navaid. Similarly, the lastground transmitter from which the aircraft is heading is marked as theFROM waypoint or navaid. Thus, prior art radio navigation systemsrequire the pilot to tune a receiver to a particular frequency and tothen fly the aircraft from transmitter to transmitter. Common radionavigation transmission systems used by the pilot community includeVORs, DMEs, TACANs, and NDBs.

VOR is an acronym for very high frequency omnidirectional range. It isthe Federal Aviation Administration's (FAA's) very high frequency (VHF)based point-to-point navigation system. VOR consists of a ground stationtransmitter and an airborne VOR receiver. The ground transmittertransmits phase encoded signals outward from the transmitter in alldirections. The airborne receiver receives the transmitted VOR signaland decodes the phase information to determine the aircraft's bearingwith respect to the ground transmitter. The aircraft's bearing isreferred as being on a particular “radial” from the VOR transmitter.Radial information is commonly displayed on a course deviation indicator(CDI) gauge or on a radio magnetic indicator (RMI) gauge. VOR is a lineof sight transmission system. As a result, VOR range is typicallylimited to 130 nautical miles at best due to the curvature of the earth.However, other obstructions can further limit the range of conventionalVOR systems. Additionally, intrinsic VOR system errors contributesubstantial error to VOR readings. At a maximum range from the VORtransmitter, errors of as much as 20 nautical miles are possible.

DME is an acronym for distance measuring equipment. DME is an activesystem requiring receivers and transmitters at both the ground stationand in the airborne aircraft. A DME system is initiated by the airborneunit sending ultra high frequency (UHF) pulses to the ground station andthe ground station sending responding UHF pulses back to the airborneunit's receiver. The airborne unit measures the time interval betweenthe initial transmission and receipt of the responding message. Themeasured time is used to calculate the distance of the aircraft from theDME station. Typically, DME stations are co-located with VOR stations ina VOR/DME station. As with VOR stations DME systems also suffer fromsignificant error. Furthermore, due to the interactive nature of DMEsystems, DME stations can become overloaded in congested airspaceenvironments.

TACAN is an acronym for tactical air navigation. TACAN is the militarycounterpart to combination VOR/DME stations. TACAN operation is verysimilar to VOR/MDME operation, where the pilot receives both directionand range indications on the aircraft instrument gauges. TACAN, likeother radio navigation systems, has error associated therewith. In fact,TACAN accuracy is only slightly better than VOR/DME.

NDB is the acronym for non-directional radio beacons. Although NDBs aretypically not used for general air navigation in the continental UnitedStates, NDBs are still used in many less developed regions of the world.Thus, NDBs remain an important part of instrument approaches for manypilots. Pilots typically use NDBs as compass locators to aid in findingthe initial approach point of an instrument landing system. NDBs arealso used for nonprecision approaches at low-traffic density airportswithout conventional VOR approaches. In a NDB system, the direction, orbearing, of the aircraft with respect to the transmitting ground stationis generally displayed on a compass card gauge by means of a pointer. AnNDB systems is not as accurate as a VOR system. Additionally, NDB radiosignals are subject to many propagational and atmospheric degradationswhich further reduce the accuracy of the NDB system. Hence existingradio navigation systems have considerable errors and inaccuraciesassociated therewith.

In addition to being familiar with certain radio navigation systems,pilots have been extensively trained on certain radio navigationinstrumentation devices. As a result of their initial training andongoing use of such radio navigation devices, many pilots resist usingnew navigation systems and/or new navigation instrumentation devices.Thus, even though conventional radio navigation systems may have errorsand inaccuracies associated therewith many pilots are reluctant to giveup familiar instrumentation devices.

As yet another drawback, in a radio navigation system, a pilot navigatesthe aircraft along a route which extends from one radio transmitter toanother radio transmitter and so on, until the aircraft reaches thedesired location. As a result pilots are often forced to travel along acircuitous route to reach a desired destination. Prior Art FIG. 1 is anexample of an airway navigation en route chart. On the chart, airwaysare represented as lines between stations 100. For example, to fly fromHelena 102 to Jackson 104 using the airway system, a pilot would flyfrom Helena 102 to Whitehall 104 via airway V21 106. The pilot wouldthen fly the aircraft from Whitehall 104 to Dillon 108 via V21 110. Nextthe pilot would fly from Dillon 108 to Dubois 112 via V21 114. Finally,the pilot would fly from Dubois 112 to Jackson 116 via V298 118.

In an attempt to overcome shortcomings associated with radio navigationsystems, a navigation system employing the Global Positioning System(GPS) had been introduced. The use of a GPS based aircraft navigationsystem is intended to eliminate the circuitous navaid to navaid schemeused in radio navigation systems, and improve navigation accuracy. GPSbased navigation systems allow a pilot to fly from a point of origindirectly to a destination. Thus, GPS systems eliminate circuitous navaidto navaid routing schemes of radio navigation systems.

However, the conventional radio navigation airway system has been inoperation since the late 1940s. As a result, there are literallyhundreds of thousands of pilots who were trained in radio navigationusing standardized radio navigation instrumentation devices. The userinterface in radio navigation equipment, due both to the length of timethe equipment has been in use and the widespread standardization of thedisplay configuration, is basically the same now as it was 30 years ago.Hence, there is great reluctance in the pilot community to use new GPSbased navigation aids.

Additionally, aircraft built by different manufacturers have containedstandardized radio navigation equipment. Therefore, pilots could easilyswitch from an aircraft built by one manufacturer into an aircraft builtby another manufacturer. With GPS navigation receivers, different unitsbuilt by different manufacturers are to varying degrees, unique. Thatis, each manufacturer has its own special control/display arrangements.Thus, in order to effectively use these GPS products, the pilot musthave knowledge of nested menus, numerous buttons and knobs, and variousnew functions. Therefore, the pilot must learn a completely newoperating system in order effectively use present GPS based navigationdevices.

Also, in order to safely use the GPS navaids, extensive training isoften required to master the myriad of informational display techniquesand control inputs/outputs. Almost none of this training investment istransferable to other GPS navaids, since each manufacturer follows hisown protocols and configurations when designing their systems. Trainingnecessary to safely and properly operate these new GPS navaids is highlyspecialized and is very expensive. Furthermore, very few flightinstructors in the general aviation community have experience with thenewer models of GPS navaids. In addition, most general aviation pilotshave previously learned to think of navigation in terms of radial anddistance when navigating with radio navigation based equipment. To useGPS, pilots must learn to think in terms of latitude and longitude mapcoordinates. Thus, current GPS navigation products from avionicsmanufacturers are often difficult to use in the actual in flightenvironment. As a result, a very significant safety issue arises whenattempting to transition pilots from conventional radio navigation toGPS based navigation.

Thus, a need has arisen for a navigation device which eliminates theerrors associated with radio navigation systems and provides GPS levelaccuracy. A further need exists for uniform and standardized navigationinstrumentation for use with a navigation system providing GPS levelaccuracy. Yet another need exists for navigation instrumentation whichoperates with GPS level accuracy and which the pilot community will notbe reluctant to adopt.

DISCLOSURE OF THE INVENTION

The present invention provides a navigation device which eliminates theerrors associated with radio navigation systems and provides GPS levelaccuracy; the present invention provides uniform and standardizednavigation instrumentation for use with a navigation system providingGPS level accuracy; and the present invention provides navigationinstrumentation which operates with GPS level accuracy and which thepilot community will not be reluctant to adopt.

The present invention comprises a radio-navaid emulating GPS navigationsystem. More specifically, in one embodiment, the present inventionincludes a position determining system which accurately determines theposition of an aircraft. The position determining system is a GPS basedposition determining system in the present embodiment. The presentembodiment also includes a data storage device which is adapted tocontain latitude and longitude information corresponding to radio navaidlocations and the like. In the present embodiment, a processor iscoupled to the position determining system. The processor calculatesposition and navigation information using data from the data storagedevice and the location information determined by the GPS based positiondetermining system. In the present invention, a radio navaid emulatinguser interface then reports the position and navigation information tothe pilot. In so doing, the present invention provides navigationinformation with GPS level accuracy in a well known and widely acceptedradio navigation user interface. Thus, the present invention allowspilots to fully utilize the features and advantages of GPS navigationwithout requiring the pilot to spend an inordinate amount of timelearning a new navigation system. The emulation process of the presentinvention is transparent to the pilot, as the pilot operates the presentinvention as though it was a conventional, and much less accurate, radionavigation based navaid.

In one embodiment; the pilot enters a desired navaid into the presentradio navigation emulating GPS system by tuning or entering into thepresent system the frequency or three letter identifier associated withthe navaid. Such entries are typically made when the pilot is planningthe flight route. The present invention then accesses stored informationto find the precise lat-long of the navaid whose frequency or threeletter identifier the user selected. Thus, although the pilot tunes orselects a ground based transmitter when using the present invention, thepilot is actually selecting a virtual station. That is, instead ofactually tuning in the frequency entered by the pilot, the presentinvention determines the lat-long information of the selected navaid.Therefore, the pilot operates the controls of the present invention inthe same manner as a pilot would operate a radio navigation device. As aresult, to the pilot, the present invention appears to be functioningthe same as a radio navigation system functions. In the presentembodiment a display of the present invention will also display theletters identifying the station having the selected frequency.Additionally, the present embodiment also displays the latlong of theselected navaid. The present invention uses the position information ofthe aircraft to calculate the bearing to the selected navaid from thepresent location of the aircraft. The bearing pointer will indicateexact bearing to the navaid selected by the pilot. Thus, the presentinvention calculates the bearing from the precise lat-long of theaircraft to the precise lat-long of selected navaid. Thus, the presentinvention provides satellite based accuracy levels in what appears tothe pilot to be a radio navigation system. As yet another advantage, thepresent invention does not have the inherent range limitationsassociated with prior art radio navigation systems. That is, the presentinvention compares the lat-long of the navaid with the lat-long of theaircraft to indicate the bearing from the aircraft to the navaid. Thepresent invention eliminates the need to receive radio signals from thenavaid before a bearing can be calculated. Hence, the present inventionis not limited by the radio signal range of a navaid. Therefore, therange of the present invention is not limited. Therefore, the presentinvention can accurately provide a bearing from the aircraft to a navaidlocated well beyond the range of radio signals. Consequently, thepresent invention provides direct routing over an unlimited distance.Thus, the benefit of direct routing will be retained in a system whichappears to the pilot to be a radio navigation based system. All of theaforementioned benefits are realized without requiring re-training ofthe pilot.

Other advantages of the present invention will no doubt become obviousto those of ordinary skill in the art after having read the followingdetailed description of the preferred embodiments which are illustratedin the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention:

FIG. 1 is a Prior Art radio navigation en route navigation chart.

FIG. 2 is a logical representation of an exemplary computer system usedas a part of a radio-navaid emulating GPS navigation system inaccordance with the present invention.

FIG. 3 is a logical diagram of a radio-navaid emulating GPS navigationsystem in accordance with the present claimed invention.

FIG. 4 is a schematic diagram of steps performed in accordance with thepresent claimed invention.

FIGS. 5A and 5B illustrate an annunciator panel and an instrument frontpanel, respectively, in accordance with the present claimed invention.

FIG. 6 is an illustration of a CDI gauge which is driven by aradionavaid emulating GPS navigation system in accordance with thepresent claimed invention.

FIG. 7 is an illustration of a combination CDI/HSI gauge which is drivenby a radio-navaid emulating GPS navigation system in accordance with thepresent claimed invention.

FIG. 8 is an illustration of an ADF gauge which is driven by aradionavaid emulating GPS navigation system in accordance with thepresent claimed invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific-details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be obvious toone of ordinary skill in the art that the present invention may bepracticed without these specific details. In other instances, well knownmethods, procedures, components, and circuits have not been described indetail as not to unnecessarily obscure aspects of the present invention.

Some portions of the detailed descriptions which follow are presented interms of procedures, logic blocks, processing, and other symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the means used by thoseskilled in the data processing arts to most effectively convey thesubstance of their work to others skilled in the art. In the presentapplication, a procedure, logic block, process, etc., is conceived to bea self-consistent sequence of steps or instructions leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated in a computersystem. It has proven convenient at times, principally for reasons ofcommon usage, to refer to these signals as bits, values, elements,symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present invention,discussions utilizing terms such as “calculating”, “accessing”,“retrieving” or the like, refer to the actions and processes of acomputer system, or similar electronic computing device. The computersystem or similar electronic computing device manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage, transmission, or display devices. Thepresent invention is also well suited to the use of other computersystems such as, for example, optical and mechanical computers.

Computer System Environment of the Present Invention

With reference now to FIG. 2, portions of the present invention arecomprised of computer executable instructions which reside in a computersystem. FIG. 2 illustrates an exemplary computer system 200 used as apart of a radio navigation emulating GPS based navigation system inaccordance with the present invention. Computer system 200 of FIG. 2includes an address/data bus 202 for communicating information, aprocessor 204 coupled to bus 202 for processing information andinstructions. Computer system 200 also incudes data storage devices suchas computer readable volatile memory unit 206 (e.g., RAM memory), and acomputer readable non-volatile memory unit 208 (e.g., ROM, EPROM,EEPROM, PROM, flash memory, programmed antifuses, etc.). Both volatilememory unit 206 and non-volatile memory unit 208 are coupled to bus 202.An optional input/output signal unit 210 and another computer readabledata storage unit 212 (e.g., a high capacity magnetic and/or opticaldisk drive) are both coupled to bus 202. Input/output signal unit 210allows bus 202 to communicate externally with other devices. Proceduresof the present invention, described below, are implemented as programcode stored within the above referenced computer readable memories andexecuted by,processor 204.

General Description of the of the Present Invention

With reference now to FIG. 3, a logical diagram 300 illustrating oneembodiment of the present invention is shown. A position determiningsystem (PDS) 300, including a signal receiver 304 and a signal processor306, is coupled to computer system 200. Signal receiver 304 receivesposition information signals and transfers the position informationsignals to signal processor 306. Signal processor 306 then generatesposition information indicative of the location of the aircraft.Position determining system 302 generates position informationindicating, for example, the latitude, longitude, altitude, and velocityof an aircraft. Position determining system 302 also accuratelydetermines the time at which the aircraft is at a specific location. Itwill be understood by those of ordinary skill in the art that numerousother well known features are not shown for purposes of clarity. Suchwell known features include but are not limited to, processing logic,user controls, power circuitry, and the like. In the present invention,position determining system 302 is, for example, a satellite-based radionavigation system. Satellite-based radio navigation systems such as theGlobal Positioning System (GPS), the Global Orbiting Navigational System(GLONASS), and the like are well suited for use with the presentinvention. Additionally, the present invention is also well suited torecording GPS ephemeris data. The present invention is also well suitedto being used in conjunction with improved position determining accuracyprovided by the impending wide area augmentation system (WAAS).

The present invention further includes a radio navigation emulating userinterface 308. In the present embodiment, radio navigation emulatinguser interface 308 includes user controls 310 and displays 312. Usercontrols 310 and displays 312, of the present embodiment, have the sameor similar design and operation parameters as standard radio navigationuser controls and displays. A detailed description of user controls 310and displays 312 is given below.

With reference next to FIG. 4, a schematic diagram 400 of stepsperformed by the present invention is shown. As shown in step 402 ofFIG. 4 a pilot or user initiates the present invention by activating anemulation mode button of user controls 310 of FIG. 3. The activation ofemulation mode overrides standard radio navigation functions and insteaduses satellite signals but in a manner which emulates the operation of aradio navigation device. That is, in the present embodiment, the presentinvention is able to function as a standard radio navigation instrumentor a satellite based navigation instrument. The present invention isalso well suited to operating as a standard satellite based navigationsystem until the emulation mode is activated. In such an embodiment,once the emulation mode is activated, the present invention continues touse satellite signals but in a manner which emulates the operation of aradio navigation device.

Next, as shown in step 404, after activating emulation mode, the pilotselects the desired navaid (e.g. a VOR, TACAN, DME, and the like) bytuning or entering the frequency associated with the navaid into thepresent system. Such entries are typically made when the pilot isplanning the flight route. The present invention is also well suited tohaving the navaids entered at various other times as well. Additionally,the following discussion relates to a VOR emulation mode, however, thepresent invention is also well suited to operating under a VORTAC,TACAN, VOR/DME, NDB, or any other conventional navaid emulation mode.The present invention is also well suited to having the pilot enterother navaid identifying information such as the three letter identifierassociated with most ground based navaids. Likewise, the presentinvention is well suited to allowing the pilot to enter a waypoint,landmark, other destination. It is anticipated that in the future, GPSonly approaches will be defined by a waypoint. In such an instance, thepresent invention is also allows that waypoint to be selected by thepilot so that the landing approach will be flown as though it were a VORapproach.

In step 406, processor 204 of FIG. 3 retrieves latitude and longitudeinformation (lat-long) corresponding to the selected navaid. That is,the present invention accesses stored information to find the preciselat-long of the navaid whose frequency or three letter identifier theuser selected. Position information for navaids is stored, for example,in da storage unit 212, volatile memory 206, or non volatile memory 208,all of FIG. 3. In the present embodiment, the present invention containsan internal database of 1000 user waypoints and 100 flight plans. Thepresent invention is also well suited to accessing navaid informationcoupled to system 300 via a portable memory devices such as a CD ROM, aPCMCIA card, and the like. In the present embodiment, the presentinvention accommodates portable memory devices such as, for example,data cards with a capacity of up to 16 megabytes. The present inventionfurther accommodate a data card with both read and write capabilities.The data cards are used to update the present radio navigation emulatingGPS system with regard to facilities, navaids, approaches, and the like,in the specific area of interest in which the pilot is flying. Thepresent embodiment further allows the user to extract and reinsert thedata card while the present invention is powered, without affecting thesystem.

Thus, although the pilot tunes or'selects a ground based transmitterwhen using the present invention, the pilot is actually selecting avirtual station. When in emulation mode, instead of actually tuning inthe frequency entered by the pilot, the present invention determines thelat-long information of the selected navaid. Therefore, the pilotoperates the controls of the present invention in the same manner as apilot would operate a radio navigation device. As a result, to thepilot, the present invention appears to be functioning the same as aradio navigation system functions. In an embodiment, in which the pilotenters a waypoint or landmark not having a conventional radio navaidassociated therewith, the present invention further contains lat-longinformation corresponding to the waypoint or landmark.

Referring now to step 408, in the present embodiment, a display 312 ofthe present invention will also display the letters identifying thestation having the selected frequency. Additionally, the presentembodiment also displays the lat-long of the selected navaid. Althoughsuch information is displayed in the present embodiment, the presentinvention is also well suited, for example, to displaying only,information typically displayed by conventional radio navigationsystems.

At step 410, processor 204 accesses the present position informationprovided by position determining system 302 of FIG. 3. The positioninformation includes the precise current lat-long of the aircraft.Position determining system 302 is also able to generate velocityinformation for the aircraft. Velocity information is obtained bymeasuring the Doppler shift of signals between position determiningsystem 10 and at least one satellite. Additionally, position determiningsystem 302 is able to very accurately determine the time at which theaircraft is at any specific location.

In step 412 of FIG. 4, processor 204 of the present invention uses theposition information to calculate the bearing to the selected navaidfrom the present location of the aircraft. The bearing pointer willindicate exact bearing to the navaid selected by the pilot. Thus, thepresent invention calculates the bearing from the precise lat-long ofthe aircraft to the precise lat-long of selected navaid. Thus, thepresent invention provides satellite based accuracy levels in whatappears to the pilot to be a radio navigation system. As yet anotheradvantage, the present invention does not have the inherent rangelimitations associated with prior art radio navigation systems. That is,the present invention compares the lat-long of the navaid with thelat-long of the aircraft to incate the bearing from the aircraft to thenavaid. The present invention eliminates the need to receive radiosignals from the navaid before a bearing can be calculated. Hence, thepresent invention is not limited by the radio signal range of a navaid.As mentioned above, most radio navaids are limited to a maximum range ofapproximately 130 nautical miles. The range of the present invention isnot limited. Therefore, the present invention can accurately provide abearing from the aircraft to a navaid located well beyond the range ofradio signals. Consequently, the present invention provides directrouting over an unlimited distance. Thus, the benefit of direct routingwill be retained in a system which appears to the pilot to be a radionavigation based system. All of the aforementioned benefits are realizedwithout requiring re-training of the pilot.

As shown in step 414, processor 204 calculates the distance to theselected navaid from the present location of the aircraft. Morespecifically, the present invention calculates the distance from theprecise lat-long of the aircraft to the precise lat-long of selectednavaid. If one embodiment, the distance to the selected navaid isdisplayed on displays 312 of FIG. 3. Thus, the present inventionprovides satellite based accuracy levels in what appears to the pilot tobe a radio navigation system. Again, the present invention does not havethe inherent range limitations associated with prior art radionavigation systems. That is, the present invention compares the lat-longof the navaid with the lat-long of the aircraft to indicate the distancefrom the aircraft to the navaid. The present invention eliminates theneed to receive radio signals from the navaid before a distance can becalculated. Hence, the present invention is not limited by the radiosignal range of a navaid. As mentioned above, the benefit of directrouting will be retained in a system which appears to the pilot to be aradio navigation based system, and no re-training of the pilot isrequired. As an additional advantage, the distance calculating abilityof the present invention allows an NDB approach to be flown as thoughthe NDB were a VOR station.

As shown in steps 416 and 418, in emulation mode, the present inventiondrives conventional radio navigation displays. The pilot then uses theconventional displays and gauges to navigate the aircraft. Thus, thepresent invention allows pilots to navigate using conventionalinstrument flight rules (IFR) instrumentation but with a level ofaccuracy and precision not found in conventional radio navigationsystems. Hence the present invention greatly enhances the situationalawareness of the uncomfortable or task saturated pilot. The presentinvention, when in emulation mode, will be safer than the conventionalradio navigation only receivers. The improved safety results, in part,because the present invention is far more accurate than radio navigationreceivers and because the present invention is not subject to range andline-of-sight limitations associated with ground based radio navaidtransmitters. Additionally, by allowing the pilot to navigate and fly adirect, straight line path to a point hundreds of miles away, thepresent invention reduces the number of times navigation informationmust be entered by the pilot. Thus, the present invention reduces thechances for erroneous navaid entries or selections. Finally, should apilot feel uncomfortable, for any reason, while operating the presentinvention in emulation mode, emulation mode can readily be deactivatedthereby placing the system back in standard radio navigation or GPSmode.

As yet another benefit, the availability of emuation mode will ease thetransition of current pilots into the operational characteristics of GPSreceivers. Pilots will be able to learn and experience the newcapabilities of the present invention at their own pace. Pilots willgain familiarity and comfort with the GPS features of the presentinvention as they use it inflight. Pilots will not have to fear enteringcongested flying areas or flying through bad weather IFX conditionswithout being completely and totally familiar with all GPS features andcontrols of the present invention. At any time in flight, the ease ofuse and familiarity of conventional navaids will be available to thetask saturated pilot. Thus, a pilot will be able to purchase the presentinvention, have it installed in an aircraft, and be able to safely andcompetently fly the aircraft, without any formalized expensive trainingwhatsoever.

Furthermore, the present invention is fully compliant with all currentTSO-C129 requirements. TSO-C129 is a standard imposed on the aviationcommunity by the Federal Aviation Administration (FAA). Ali avionicscomponents must comply with the TSO-C129 standard before the FAA willapprove the use of the components. The exact specifications of theTSO-C129 standard are well known in the aviation community.

As yet another advantage, the present invention is also well suited touse with receiver autonomous integrity monitoring (RAIM) algorithms. InGPS receivers, RAIM algorithms perform an independent check of thevalidity of a GPS position fix. Such validity checks are necessary toinsure that air navigation using GPS signals can safely occur. If theRAIM algorithm determines that the GPS signal reliability falls beneatha predetermined threshold, the present invention sounds an alarm. Uponhearing or seeing the alarm, a use of the present invention knows thatconventional navaids must be used for navigation.

Detailed Description of User Controls and Displays

FIGS. 5A and 5B illustrate an exemplary annunciator panel 500 and anexemplary instrument front panel 502, respectively, used by the presentradio navigation emulating GPS system. It will be understood by those ofordinary skill in the art that the present invention is well suited tonumerous variations in the layout of an exemplary annunciator panel 500and an exemplary front panel 502.

With reference again to FIG. 5A, annunciator panel 500 has a pluralityof switches and buttons. A description of exemplary switches and buttonsin the present radio navigation emulating GPS system is given below.Again, it will be understood by those of ordinary skill in the art thatthe present invention is also well suited to numerous variations in thelayout, function, and type of switches and buttons used in the presentinvention.

NAV/GPS 504 is an alternate action switch which will select either radionavigation (NAV) or GPS information to drive an external CDI, ahorizontal situation indicator (HSI), or a moving map. In the presentembodiment, NAV/GPS 504 is backlit. If NAV is selected, external radionavigation signals are used to compute the navigation data. If GPS isselected, GPS information is used to compute navigation data.

CDI/FP 506 is a momentary switch which is used to toggle betweenEmulation mode and flight plan mode. Flight plan mode is used to programwaypoints for navigation. Emulation mode immediately switches thedisplay to navigation data. In the present embodiment, CDI/FPL 506switch is backlit.

APR/ARM 508 is a switch which is used for an approach. APR/ARM 508flashes when an approach can be armed. After the approach has beenarmed, APR/ARM 508 will be lit continuously. If no approach is selectedor the approach cannot be armed, APR/ARM 508 is not backlit. When anapproach is armed the present invention automatically sequences itsdisplay to show approach information when the initial approach point isreached. The approach can be armed when the present navigation systemdetermines that the approach may be safely flown.

VTF 510 is an alternate action switch which switches the presentinvention between flight plan approach mode and Vector-To-Final approachmode. VTF 510 is backlit continuously whenever an approach has beenarmed (and can therefore be switched into VTF mode). In Vector-to-Finalthe navigator will indicate navigation data to the final approach pointof an approach.

LAMP TEST 512 is a momentary switch which tests all indicators andlights. LAMP TEST 512 is used to insure that all annunciator panel lampsare functioning properly. When LAMP TEST 512 is depressed all lights andindicators illuminate momentarily.

With reference again to FIG. 5A, annunciator 500 has a plurality ofannunciators/indicator lights. A description of the exemplaryannunciators in the present radio navigation emulating GPS system isgiven below. Again, it will be understood by those of ordinary skill inthe art that the present invention is also well suited to numerousvariations in the layout, function, and type of annunciators used in thepresent invention.

NAV 514 indicates that currently, the CDI, HSI, or moving map isdisplaying information from an external Nav or Nav/Comm radio. Thisannunciator is driven directly from the NAV/GPS switch. It tells thepilot what source the CDI, HSI, or radio magnetic indicator (RMI) isusing to generate their navigation indications. If NAV 514 is lit, anon-GPS source is selected (external navaid).

GPS 516 indicates that currently, the CDI, HSI, or moving map isdisplaying GPS derived information. This annunciator is driven directlyfrom NAV/GPS switch 504. If GPS is lit, GPS derived position informationis selected.

CDI 518 indicates that the present invention is in VOR Emulation mode.

FPL 520 indicates that currently, the present invention is in flightplan mode.

APR/ACT 522 indicates that the approach mode is active. The approachmode is active, for example, during the period of time when the aircraftis within 2 nautical miles from a final approach fix until the aircraftis landed or until the approach is canceled. When the approach mode isactive, the present invention is providing approach information to thepilot.

HOLD 524 indicates that the present radio navigation emulating GPSsystem is providing guidance for flying the aircraft through a holdingpattern. HOLD 525 is illuminated when the pilot selects HOLD button 525on the front panel 502 of FIG. 5B. The pilot then flies the hold patternindicated by the present invention.

WPT 526 indicates that the aircraft is close to the current “TO”waypoint. This warns the pilot that the Navigator will soon switch tothe next waypoint in the flight plan.

VTF 528 indicates that the present radio navigation emulating GPS systemis in Vector-To-Final mode. VTF 528 is driven directly by VTF switch510.

MSG 530 indicates that a new message is available on the present radionavigation emulating GPS system. Messages from the present invention mayindicate system status, waypoint information, navaid information, orother information requiring the pilot's attention.

PTK 532 indicates that an offset track has been selected on the presentradio navigation emulating GPS system.

DR 534 indicates that the present radio navion emulating GPS system isin Dead Reckoning mode. Dead Reckoning refers to determining positionusing only heading, time, and speed.

NO RAIM 536 indicates that the present radio navigation emulating GPSsystem has lost the capability for integrity monitoring. RAIM is aTSO-C129 requirement standard for monitoring the integrity of GPSsatellite signals.

With reference next to FIG. 5B, front panel 502 has a graphics-capablemulti-function display 538, and plurality of control knobs and buttons.A description of the exemplary graphics-capable multi-function display,and plurality of control knobs and buttons of the present radionavigation emulating GPS system is given below. Again, it will beunderstood by those of ordinary skill in the art that the presentinvention is also well suited to having numerous variations in thelayout, function, and type of graphics-capable multi-function display,and plurality of control knobs and buttons used in the presentinvention.

As shown in FIG. 5B, the center of front panel 502 includes agraphics-capable multi-function display 538. The controls to the rightof graphics-capable multi-function display 538 are used for navigationfunctions. The controls to the left of graphics-capable multi-functiondisplay 538 are used to control a communications radio. Although acommunication radio is shown in the present embodiment, the presentinvention is also well suited to not having a communications radiointegral therewith. The functions of the control knobs and buttonsdepends on the selected mode of the present invention.

When using any of the functions provided by depressing the NRST/DBAS540, HELP/AUX 542, and EDIT 544 keys, pushing the NAV 546 key returnsthe graphics-capable multi-function display 538 to the NAV page format,without accepting any changes or inputs made to an active or standbywaypoint. The NAV page format typically displays navigation informationfor a current route to the pilot. The present invention displays thefollowing information on graphics-capable multi-function display 538when in the NAV page format:

Active “VOR frequency or NDB frequency,

Active fix identifier;

Standby “VOR frequency” or “NDB frequency;

Standby fix identifier;

Distance to active fix (similar to DME distance);

Bearing to active fix;

ETA to active fix;

Distance to standby fix (similar to DME distance).

The navigation information displayed in the present embodiment is thestandard configuration used in most radio navigation systems. As such,the present embodiment provides information in a manner which isfamiliar to most pilots. Using graphics-capable multi-function display538 the present invention is able to emulate any conventional navaid.

When the unit is displaying the NAV page, the two concentric knobs NAV548 and NAV 550 to the left of the graphics-capable multi-functiondisplay 538, are used to edit the standby information selected navaids.Knobs NAV 548 and NAV 550 are used to tune or select, for example, a VORor NDB frequency or a fix identifier. When the present invention is inVOR emulation mode, to select a VOR frequency, NAV 550 is used to tunethe standby VOR frequency. NAV 548 used to tune the 100 kHz and 10 kHzdigits. Likewise, when the present invention is in NDB emulation mode,NAV 550 is used to tune the standby NDB frequency 100 kHz digit. NAV 548is used to tune the 10 kHz and 1 kHz digits. As far as the user isconcerned, tuning of the present invention is handled the same as tuningof a radio navigation based system. If no lat-long information is foundcorresponding to the selected navaid, the present invention displaysdashes on all fields relating to the standby fix on graphics-capablemulti-function display 538. Slot 552 is adapted to receive a portablememory device such as a CD ROM, a PCMCIA card, and the like. Theportable memory device is used to update the present radio navigationemulating GPS system with regard to facilities, navaids, approaches, andthe like, in the specific area of interest in which the pilot is flying.

Thus, the present invention achieves all emulation modes using astandard configuration on graphics-capable multi-function display 538.The pilot selects the desired emulation mode through manipulation of thecontrols described above. The present invention communicates betweenfront panel 502 and annunciator panel 500 using discrete inputs. Theinputs, in turn, inform the pilot of status of the present invention andprovide indications as to the present invention's current mode. Thus,the present radio navigation emulating GPS system provides the pilotwith the full features of highly accurate GPS navigation, and providesthe comfort and security of conventional radio navaid emulation at thetouch of a button. Thus, the present invention allows pilots to fullyutilize the features and advantages of GPS navigation without requiringthat the pilot spend an inordinate amount of time head down, as opposedto being head up and flying the airplane. The present invention furtherminimizes up-front training costs as the most pilots are alreadyfamiliar which the type of operation embed by the present invention.Additionally, the present invention achieves the accuracy of GPS andgreatly improves the standard methods of conventional navaid navigation.A pilot will have GPS accuracy and flexibility while operating thepresent invention as though it were a conventional, and much lessaccurate, radio navaid.

With reference still to FIG. 5B, two concentric knobs COM 554 and COM556 to the left of graphics-capable multi-function display 538 are usedsolely to edit the communications (comm) radio standby frequency. COM556 is used to change the MHz and 10 MHz digits, and COM 554 is used tochange the 10 kHz and 100 kHz digits. Button 558 marked “⇄”to the leftof graphics-capable multi-function display 538 and under knobs COM 554and COM 556, is used to swap standby and active frequencies in the commradio. This allows the pilot to switch between approach control andtower, for instance. The comm radio of the present invention furtherincludes a volume and on/off control 560.

The present invention also displays the position of the aircraft withrespect to selected bearing using a course deviation indicator (CDI) 600shown in FIG. 6. A CDI is a common cockpit navigation display device inuse today. All pilots familiar with radio navigation are familiar withthe use of a standalone CDI 600, or a combination CDI such as a CDI/HSI(horizontal situation indicator) 700 as shown in FIG. 7. That is, onceemulation mode is activated, the present invention will emulate the useof a radio navigation based system and display the relative location ofthe aircraft with respect to a selected route on, for example, CDI/HSI700. In addition, in the present embodiment, the present invention canalso provide a constant read out of distance from the selected navaid,in the same manner a conventional DME receiver does today. Thus, the enduser will receive information that emulates, for example, both a VORreceiver and a DME receiver.

With reference next to FIG. 8, when emulating an NDB radio navigationsystem, the present invention also emulates NDB indications on anautomatic direction finder (ADF) 800. When emulating other radionavaids, the present invention emulates the respective radio navaidindications on ADF 800 when appropriate.

The entire emulation process achieved by the present invention istransparent to the pilot. Emulation mode will be easily accessible andintuitively obvious in its operation. When the emulation mode isde-activated, the present invention instantly switches to conventionalradio navaid operation.

Thus, the present invention provides a navigation device whicheliminates the errors associated with radio navigation systems andprovides GPS level accuracy. The present invention also provides auniform and standardized navigation instrumentation for use with anavigation system providing GPS level accuracy. As yet anotheradvantage, the present invention also provides a navigationinstrumentation which operates with GPS level accuracy and which thepilot community will not be reluctant to adopt.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are noended to be exhaustive or to limit the inventionto the precise forms disclosed, and obviously many modifications andvariations are possible in light of the above teaching. The embodimentswere chosen and described in order to best explain the principles of theinvention and its practical application, to thereby enable othersskilled in the art to best utilize the invention and various embodimentswith various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the claims appended hereto and their equivalents.

What is claimed is:
 1. A computer implemented method of emulating aconventional radio navigation system while using satellite basedposition information, the method comprising the computer implementedsteps of: receiving an identifier associated with a conventional navaid;retrieving coordinates corresponding to a location of the conventionalnavaid; generating satellite based position information for an aircraft;generating navigation information for the aircraft using the location ofthe conventional navaid and the satellite based position information forthe aircraft; and driving a display of a conventional radio navigationdevice by using the navigation information.
 2. The apparatus of claim 1,wherein the device is a CDI (course deviation indicator) device.
 3. Theapparatus of claim 1, wherein the device is an HSI (horizontal situationindicator) device.
 4. The apparatus of claim 1, wherein the device is anADF (automatic direction finder) device.
 5. The apparatus of claim 1,wherein the guidance indications are generated without requiring asignal from a radio navaid.